Direct current powered ignition system with blocking oscillator

ABSTRACT

An electrical system for igniting fuel in a turbine engine or the like which utilizes a battery-powered blocking oscillator and a transformer having its primary winding in the oscillator circuit and its secondary winding connected to a spark plug that ignites fuel in the engine.

nited States Patent 91 McKeown 51 May 1, 1973 [54] DIRECT CURRENT POWERED [56] References Cited I NIT] N SY TEM 1TH BL IN b f w OCK G UNITED STATES PATENTS [75] Inventor: James E. Sidney, N'Yl 3,535,652 10/1970 Minks ..3l5/209 X [7 3] Assignee: The Bendix Corporation, Southfield, Primary Examiner-Roy Lake Mi h Assistant Examiner-Lawrence J. Dahl [22] Filed Feb 25 19 2 Att0meyRaymond J. Eifler et al.

[21] Appl. No.: 229,332 RACT An electrical system for igniting fuel in a turbine en- [52] Cl. 315/209 T, 123/148 E 315/209 R gine or the like which utilizes a battery-powered 315/211 331/1 blocking oscillator and a transformer having its prima- [51] um Cl 6 37/02 ry winding in the oscillator circuit and its secondary Fie'ld B 148 winding connected to a spark plug that ignites fuel in the engine.

4 Claims, 2 Drawing Figures AMT DIRECT CURRENT POWERED IGNITION SYSTEM WITH BLOCKING OSCILLATOR BACKGROUND OF THE INVENTION This invention relates to an ignition system for an automobile turbine engine and more particularly to the electrical circuitry associated therewith.

Basically, automobile ignition system include a source of d-c power, an oscillator, a transformer responsive to the oscillator for stepping up the pulses therefrom, and a secondary circuit which includes a spark gap discharge device located in the combustion chamber of the engine. In this type of circuit the impedance of the spark gap discharge device (spark plug) varies (open circuit to short circuit). Also, this type of circuit generally includes a transformer which has a control winding (tertiary) that experiences high frequency oscillations that affect the operation of the circuit and, therefore, the maximum power that can be transferred to the spark plug. The high frequency oscillations occur because the amount of feedback to the control winding that turns OFF the switching transistor in series with the primary winding depends upon the voltage across the secondary winding in parallel with the spark plug. At certain load conditions the feedback to the control winding is frequently insufficient to overcome a positive bias on the switching transistor. Therefore, the switching transistor is OFF for very short intervals, hence high frequency oscillations. These high frequency oscillations are therefore undesirable in an ignition system because the discharge at the spark plug 160, necessary to ignite the fuel in the engine, may be extinguished.

SUMMARY OF THE INVENTION This invention provides an ignition system for a turbine engine that is not subject to high frequency oscillations as a result of variations in the impedance of the load and provides a shower of sparks to ignite fuel in the engine.

The invention is an ignition system for an automobile turbine engine that is characterized by a battery powered blocking oscillator in combination with a 2- 0 vide an electrical apparatus for creating electrical winding transformer having a spark plug across the a secondary winding thereof for igniting the fuel in the engine. I

In the embodiment of this invention the electrical circuit comprises: a battery; a transformer having a primary winding connected to the battery and a secondary winding connected to a spark plug; an oscillator circuit connected to the battery and the transformer to intermittently interrupt current flow from the battery through the primary winding to cause an electrical discharge at said spark plug to ignite fuel in the engine.

This circuit eliminates the need for a transformer having a control winding and utilizes a transistor in series with the transformer winding so that the oscillating circuit is virtually independent of the load on the secondary of the transformer.

The circuit makes possible control over the frequency of oscillations of the oscillator circuit by employing an unconventional feedback technique that does not use a 3-winding transformer but instead uses a 2-winding transformer in combination with a blocking oscillator.

sparks or arcs that are adapted to ignite combustible materials.

Another object is to provide an ignition system that is economical to make, has few parts, and is reliable.

The above and other objects and features of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings and claims which form a part of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. Tis a schematic diagram of a d-c powered ignition system that accomplishes the objects of this invention.

FIG. 2 is a schematic diagram of an alternate embodiment of the circuit shown in FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a preferred embodiment of the cir cuit that embodies the principles of this invention.

A solid state switch oscillator (blocking oscillator) shown within the dotted lines is powered by a battery or other direct current source. A transformer has its primary winding 101 connected into the oscillator circuit 100 and its secondary winding 151 connected to a spark gap to dissipate the energy generated by the oscillator 100 when the switch 14-1 is closed. The windings 101 and .151 of the transformer 150 are inductively coupled and wound and disposed in the manner indicated by the dots.

The solid state switch oscillator 100 operates to intermittently interrupt current flow from the battery 140 through the primary winding 101 of the transformer 150 and includes a first switching transistor 103, a first voltage divider network (110, 111, 112, 113, 114), a second voltage divider network (121, 122, 123), and first diode means (102, 104, 106) connected between the first voltage divider network and the primary winding 101 of the transformer 150 to direct the flow of current to and from the primary winding 101. The oscillator circuit shown is capable of producing oscillations in the range of 800 to 2,000 Hz.

The first voltage divider network includes a diode 110 and a plurality of resistors 111, 112 and 113 connected together in series across the primary winding 101 of the transformer and the first transistor 103. Capacitor 114 is in parallelwith diode 110 and the emitter-base junction of transistor 121 to back bias transistor 121 (OFF) during the transfer of energy from the primary winding 101 of transformer 150 to the secondary winding 151.

The diode means that directs the current from the primary winding 101 includes a first diode 102 connected by its anode terminal to the junction between resistor 111 and resistor 112 and its cathode connected to the junction between the primary winding 101 and the first transistor 103. To permit current to flow from the primary winding 101 when transistor 103 is OFF, diodes 104 and 106 are connected in series with one anode terminal connected to the junction between the primary winding 101 and the first transistor 103 and one cathode terminal connected to the junction between the second transistor 1 12 and the third resistor 113.

The second voltage divider network includes a transistor 121, a resistor 122 and a resistor 123 connected together in series across the battery 140. The base of the first transistor 121 is connected, for biasing purposes, to the junction between the diode 110 and resistor 111 of the first voltage divider network. The base of the first transistor 103 is connected tothe junction between resistors 122 and 123 to receive a current at the base of transistor 103 when the transistor 121 is in the conductive state.

The secondary winding 151 of the transformer 150 is connected to a spark gap device, such as a spark plug, 160. When the battery 140 is 4 to 6 volts, the maximum open circuit voltage that can be obtained across the gap 160 is KV to 30 KV which is determined by transformer ratio and circuit losses. However, this voltage is limited by the breakdown voltage of the gap 160 and is generally about 12 to 15 K volts.

In one satisfactorily operable system of the circuit shown in FIG. 1 the elements of the circuit had the values or were of the types indicated below:

Battery 140 Resistor 122 Resistor 123 Resistor 111 ohms, 9% watt Resistor 112 1K ohms, A watt Resistor 113 lOK ohms. l/Z watt Diode Type GEA14F Diode 102 Type GEA14F Diode 104 Type GEAl4F Diode 106 Type GEAMF Transistor 103 Type 2N3055 Transistor 121 Motorola Type MJE 37l V Transformer Bg djig Qorp. Part No. l0-94078-l Primary 240T 24 7 volts Secondary 29000T No. 42 25,000 volts Switch 141 Ignition switch Spark Gap 160 Spark plug OPERATION Referring now to FIG. 1, the circuit operates as follows: when switch 141 is closed, a positive voltage is applied across the emitter-base circuit of the transistor 121, and transistor 121 conducts, permitting a current to flow through resistors 122 and 123 and through lead 124 to the base of transistor 103 which is in the nonconducting state. When the current to the base of transistor 103 is sufficient, transistor 103 conducts and is turned ON. When transistor 103 is ON, current flows through the primary winding 101 of transformer 150 and transistor 103. At the same time a second current flows through emitter-base junction of transistor 121, resistor 111, diode 102 and the collector-emitter of transistor 103. This current causes transistor 121 to saturate. As a result of transistor 121 operating in this saturated state, a constant base current is provided to transistor 103 from transistor 121 through resistor 122 and lead 124. When the sum of the currents flowing into transistor 103 from primary winding 101 of transformer 150 and from diode 102 is equal to the product of the grounded current gain of transistor 103 multiplied by the base current to transistor 103, transistor 121 turns OFF very quickly, which turns OFF transistor 103. At this time the current flowing through primary winding 101 rapidly decays to zero, inducing a high voltage across the gap 160. The gap spacing is designed so that the voltage applied is greater than the voltage breakdown potential of the gap 160 and therefore a discharge occurs across gap 160. Simultaneously with the discharge of the energy in the transformer across spark gap 160, the primary winding becomes a current source which acts to charge capacitor 114 through diodes 104, 106 and-resistors 111, 112. The charge on capacitor 114 is therefore reversed so that transistor 121 is reversed biased. This reverse biasing assures that transistor 121 remains turned OFF for a sufficient time period to keep the operating frequency low. Once the energy in capacitor 114 discharges through diode 110 and is charged in the reverse direction by battery through resistors 111, 112, 113, transistor 121 is again forward biased and the cycle repeats itself again.

FIG. 2 illustrates an alternate embodiment of the invention that utilizes less components than the circuit shown in FIG. 1.

A solid state switch oscillator 100 (blocking oscillator) shown within the dotted lines is powered by a battery 140 or other direct current source. A transformer has its primary winding 101 connected into the oscillator circuit 100 and its secondary winding 151 connected to a spark gap device to dissipate the energy generated by the oscillator 100 when the switch 141 is closed and the oscillator is operating. The windings 101 and 151 of the transformer 150 are inductively coupled and wound and disposed in the manner indicated by the dots.

The solid state switch oscillator 100 operates to intermittently interrupt current flow from the battery 140 to the primary winding 101 of the transformer 150 and includes a first switching transistor 3, a first voltage divider network (10, 11, 13, 14), a second voltage divider network (21, 22, 23), and zener diode means 8 connected between the first voltage divider network and the junction between the primary winding 101 of the transformer 150 and transistor 3 to direct the flow of current to and from the primary winding 101 in a predetermined manner. The oscillator circuit shown is capable of producing oscillations in a range of 800 to 2,000 Hz.

The first voltage divider network includes a diode l0 and a plurality of resistors 11 and 13 connected in series across the primary winding 101 of the transformer 150 and the first transistor 3. Capacitor 14 is in parallel with diode 10 and emitter-base junction of transistor 21 to back bias transistor 21 (OFF) during the transfer of energy from the primary winding 101 of transformer 150 to the secondary winding 151.

The second voltage divider network includes a transistor 21, a resistor 22 and resistor 23 connected in series across the battery 140. The base of the first transistor 21 is connected for biasing purposes to the junction between diode 10 and resistor 11 of the first voltage divider network. The base of the first transistor 3 is connected to the junction between resistors 22 and 23 through lead 24 to receive a current at the base of transistor 3 when transistor 21 is in the conducting state ON.

The zener diode 8 that directs the current from the primary winding 101 in a predetermined manner is connected by its anode terminal to the junction between resistors 11 and 13 and by its cathode to the junction between the primary winding 101 and the first transistor 3. The zener diode has a breakdown potential of 2.4 volts which isolates the primary winding from the potential divider 10, 11, 13 for starting. Initially zener diode 8 is nonconducting; however, it breaks down at 2.5 volts. This hold-off voltage supplies the necessary initial forward biasing to turn transistor 21 ON, which turns transistor 3 ON. Zener diode 8 then conducts in the forward direction to allow more current to flow from the base of transistor 21 and allow transistor 21 to saturate, thus saturating transistor 3. This action then turns transistors 21 and 3 OFF and the energy stored in the primary 101 is transferred to the secondary 151.

The secondary winding 151 of the transformer 150 is connected to a spark gap device such as a spark plug 160. When the battery 140 is between 6 and volts, the maximum voltage that can be attained across gap 160 is about 30 K volts which is determined by the transformer ratio. However, this voltage is limited by the breakdown voltage of the gap 160 and is generally about 12-15 K volts. Diode 9 is located across the base emitter terminals of transistor 3 to prevent high negative voltage spikes from appearing across the base to emitter junction of transistor 103 and damaging the transistor.

In one satisfactorily operable system of the circuit shown in FIG. 2, the elements of the circuit had the values or were of the types indicated below:

Battery 140 6-20 volts d-c The circuit shown in FIG. 2 operates as follows: when the voltage of battery 140 is between 6 and 20 volts d-c and is applied to the circuit when switch M1 is closed, current flows through the base-emitter junction of transistor 21, resistor 11 and resistor 13 to ground. Application of a voltage to the circuit forward biases transistor 21, causing transistor 21 to turn ON and current flows through the transistor 21, resistor 22 and resistor 23 to ground. When transistor 21 is ON, current also flows through lead 24 to the base of transistor 3. This base current to transistor 3 turns transistor 3 ON, thereby developing a voltage across the winding 101. At this time zener diode 8 conducts in the forward direction, thereby allowing more current to flow from the base of transistor 21 causing it to saturate very quickly.

The flow of current continues to rise through the primary winding 101 of transformer 150 until the drive current flowing through transistor 3 through lead 24 is no longer adequate to maintain saturation of transistor 3. At this point the rise in current from the primary winding 101 ceases and the voltage across the primary winding 101 reverses itself. At this point the zener diode 8 conducts in the reverse direction causing current to flow through zener diode 8, resistor 11 and diode 10. With diode 10 conducting, transistor 21 is reversed biased OFF and therefore the base current to transistor 3 flowing through resistor 22 and lead 24 ceases to flow. This action maintains transistor 3 OFF for a predetermined time interval. Simultaneously capacitor 141 is being charged to reverse bias transistor 21 in the OFF mode. Transistor 21 is therefore maintained in the OFF mode until capacitor 14 discharges, allowing transistor 21 to be forward biased and placed in the ON mode. As inductive switching occurs in the transformer 115, Le, the energy stored in the primary is transferred to the secondary and discharged through the spark gap discharge device 160, a large voltage appears across the primary winding 101 in the reverse direction. Once the energy is dissipated by the spark discharge device 160, the primary winding 101 voltage is no longer present and the zener diode 8 no longer conducts in the reverse direction and is considered as turned OFF. When current again flows in the baseemitter junction of transistor 21, which is after capacitor 14'has dissipated its reverse charge, the cycle repeats itself again. The importance of capacitor 14 in this circuit is to delay the restarting of the oscillator as it provides a positive method of turning OFF transistor 21 for a predetermined time interval which in turn maintains transistor 3 OFF.

Although only two embodiments of the invention have been illustrated in the accompanying drawing and described in the foregoing specification, it is to be expressly understood that the invention is not limited thereto. For example, many variations which will now be apparent to those'skilled in the art may be made in the types of components and in the values thereof that have been suggested. For example, it will be apparent to skilld artisans that different types of semiconductor or solid state switching devices may be substituted for the types illustrated and that suitable variations may be made in the circuitry to accomplish the desired results in accordance with the novel method disclosed.

Accordingly, it is intended that the illustrative and descriptive materials herein be used to illustrate the principle of the invention and not to limit the scope thereof.

Having described the invention, what is claimed is:

1. in combination with a gas turbine engine of the type having a spark gap device for igniting fuel in the engine and an ignition circuit for producing an electrical discharge at the spark gap, the improvement wherein the ignition circuit comprises:

a source of d-c energy;

a transformer having a primary winding connected to said d-c source and a secondary winding, said spark gap discharge means connected across said secondary winding to discharge energy transferred from said primary winding to said secondary winding of said transformer;

switching means connected to said source and said transformer to periodically interrupt current flow from said source through said primary winding,

said switching means including:

a first transistor having collector and emitter terminals in series with said primary winding, said transistor having alternate conductive and nonconductive intervals to periodically interrupt the current flowing from said primary winding;

a first voltage divider network connected across said first transistor and said primary winding, said first voltage divider network including:

a first diode having a first terminal connected to the junction between said primary winding and said source of electrical energy and a second terminal a capacitor connected across said diode;

a first resistor in series with the second terminal of said first diode;

a second resistor in series with said first resistor;

a third resistor in series with said second resistor and having one terminal connected to the junction between said first transistor and said source of electrical energy; and

second diode means connected between the junction between resistors of the first voltage divider network and the junction between said primary winding and said first transistor to direct current from said winding in a predetermined manner; and

a second voltage divider network connected across said source of electrical energy, said second voltage divider network including means for connecting said second voltage divider network to the base of said first transistor; a second transistor having its base connected to the second terminal of said first diode and having alternate conductive and nonconductive intervals to respectively control the conductive and nonconductive intervals of said first transistor through said connecting means; and a third and fourth series connected resistor in series with said second transistor, said means for connecting said second voltage divider network to said base of said second transistor being connected to the junction between said third and fourth resistors, whereby the flow of current from said source to said primary winding is periodically interrupted causing current to flow in an oscillatory manner through said primary winding so that energy is transferred to said secondary winding and discharged by said spark gap in response to a change in the conductive state of said first transistor.

2. The electrical apparatus recited in claim 1 wherein said second diode means connected to said junction between said primary winding and said first transistor includes at least one diode connected to said junction between said first and second resistor and said junction between said first transistor and primary winding and at least one other diode connected to said junction between said second ad third resistor and the junction between said first transistor and said primary winding, said at least one other diode connected to allow current to flow in a direction opposite that of said at least one diode.

3. Electrical apparatus comprising:

a source of d-c energy;

a transformer having a primary winding connected to said d-c source and a secondary winding;

spark gap discharge means connected across said secondary winding to discharge energy transferred from said primary winding to said secondary winding of said transformer;

switching means connected to said source and said transformer to periodically interrupt current flow from said source through said primary winding, said switching means including:

a first transistor having collector and emitter electrodes in series with said primary winding, said transistor having alternate conductive and nonconductive intervals to periodically interrupt the current flowing from said primary winding;

a first voltage divider network connected across said first transistor and said primary winding, said first voltage divider network including:

a diode having a first terminal connected to the junction between said primary winding and said source of electrical energy and a second terminal connected to the base of said second transistor;

a capacitor connected across said diode;

a first resistor in series with the second terminal of said diode;

a second resistor having one terminal thereof connected in series with said first resistor and the other terminal thereof connected to the other electrode of said first transistor not connected to said primary winding; and

zener diode means having its anode connected to the junction between the first and second resistors of the first voltage divider network and its cathode connected to the junction between said primary winding and said first transistor to direct current from said winding in a predetermined manner; and

a second voltage divider network connected across said source of electrical energy and in parallel with said first voltage divider network, said second voltage divider network including:

a second transistor having its base terminal connected to the second terminal of said diode in said first voltage divider network, a second terminal of said second transistor connected to the first terminal of said second diode means and one terminal of said source of d-c energy;

a third resistor connected to the third terminal of said second transistor;

a fourth transistor connected at one end to the third resistor and at the other end to the other terminal of said source of d-c energy and said other end of said second resistor; and

means for connecting the junction between said third and fourth resistors of said second voltage divider network to the base of said first transistor, said second transistor having alternate conductive and nonconductive intervals to respectively control the conductive and nonconductive intervals of said first transistor through said connecting means whereby the flow of current from said source to said primary winding is periodically interrupted causing current to flow in an oscillatory manner through 

1. In combination with a gas turbine engine of the type having a spark gaP device for igniting fuel in the engine and an ignition circuit for producing an electrical discharge at the spark gap, the improvement wherein the ignition circuit comprises: a source of d-c energy; a transformer having a primary winding connected to said d-c source and a secondary winding, said spark gap discharge means connected across said secondary winding to discharge energy transferred from said primary winding to said secondary winding of said transformer; switching means connected to said source and said transformer to periodically interrupt current flow from said source through said primary winding, said switching means including: a first transistor having collector and emitter terminals in series with said primary winding, said transistor having alternate conductive and nonconductive intervals to periodically interrupt the current flowing from said primary winding; a first voltage divider network connected across said first transistor and said primary winding, said first voltage divider network including: a first diode having a first terminal connected to the junction between said primary winding and said source of electrical energy and a second terminal a capacitor connected across said diode; a first resistor in series with the second terminal of said first diode; a second resistor in series with said first resistor; a third resistor in series with said second resistor and having one terminal connected to the junction between said first transistor and said source of electrical energy; and second diode means connected between the junction between resistors of the first voltage divider network and the junction between said primary winding and said first transistor to direct current from said winding in a predetermined manner; and a second voltage divider network connected across said source of electrical energy, said second voltage divider network including means for connecting said second voltage divider network to the base of said first transistor; a second transistor having its base connected to the second terminal of said first diode and having alternate conductive and nonconductive intervals to respectively control the conductive and nonconductive intervals of said first transistor through said connecting means; and a third and fourth series connected resistor in series with said second transistor, said means for connecting said second voltage divider network to said base of said second transistor being connected to the junction between said third and fourth resistors, whereby the flow of current from said source to said primary winding is periodically interrupted causing current to flow in an oscillatory manner through said primary winding so that energy is transferred to said secondary winding and discharged by said spark gap in response to a change in the conductive state of said first transistor.
 2. The electrical apparatus recited in claim 1 wherein said second diode means connected to said junction between said primary winding and said first transistor includes at least one diode connected to said junction between said first and second resistor and said junction between said first transistor and primary winding and at least one other diode connected to said junction between said second ad third resistor and the junction between said first transistor and said primary winding, said at least one other diode connected to allow current to flow in a direction opposite that of said at least one diode.
 3. Electrical apparatus comprising: a source of d-c energy; a transformer having a primary winding connected to said d-c source and a secondary winding; spark gap discharge means connected across said secondary winding to discharge energy transferred from said primary winding to said secondary winding of said transformer; switching means connected to said source and said transformer to periodically interrupt current flow from said source through said primary winding, said switching meAns including: a first transistor having collector and emitter electrodes in series with said primary winding, said transistor having alternate conductive and nonconductive intervals to periodically interrupt the current flowing from said primary winding; a first voltage divider network connected across said first transistor and said primary winding, said first voltage divider network including: a diode having a first terminal connected to the junction between said primary winding and said source of electrical energy and a second terminal connected to the base of said second transistor; a capacitor connected across said diode; a first resistor in series with the second terminal of said diode; a second resistor having one terminal thereof connected in series with said first resistor and the other terminal thereof connected to the other electrode of said first transistor not connected to said primary winding; and zener diode means having its anode connected to the junction between the first and second resistors of the first voltage divider network and its cathode connected to the junction between said primary winding and said first transistor to direct current from said winding in a predetermined manner; and a second voltage divider network connected across said source of electrical energy and in parallel with said first voltage divider network, said second voltage divider network including: a second transistor having its base terminal connected to the second terminal of said diode in said first voltage divider network, a second terminal of said second transistor connected to the first terminal of said second diode means and one terminal of said source of d-c energy; a third resistor connected to the third terminal of said second transistor; a fourth transistor connected at one end to the third resistor and at the other end to the other terminal of said source of d-c energy and said other end of said second resistor; and means for connecting the junction between said third and fourth resistors of said second voltage divider network to the base of said first transistor, said second transistor having alternate conductive and nonconductive intervals to respectively control the conductive and nonconductive intervals of said first transistor through said connecting means whereby the flow of current from said source to said primary winding is periodically interrupted causing current to flow in an oscillatory manner through said primary winding so that energy is transferred to said secondary winding and discharged by said spark gap in response to a change in the conductive state of said first transistor.
 4. The electrical apparatus recited in claim 6 wherein said apparatus includes a second diode connected between the base of said first transistor and said source of d-c energy. 